As discussed in detail in the incorporated disclosure, automotive air conditioning systems are provided in most vehicles to cool the passenger compartment of the vehicle during hot weather. In general, automotive air conditioning systems comprise a compressor coupled to the engine that compresses a refrigerant to its liquid state. The compressed liquid refrigerant is then delivered to a heat exchanger known as an evaporator within the ductwork of the air conditioning system, where it is allowed to expand and thereby cools the evaporator. A blower forces air across the evaporator and into the passenger compartment of the vehicle. As the air passes through the evaporator, it is cooled and the latent heat that was contained in the air is transferred to the refrigerant within the evaporator. Thus, the passenger compartment receives cool air. The heated refrigerant is then passed through a radiator where it is cooled and delivered back to the compressor where the cycle begins anew.
As warm air from the passenger compartment is blown through the evaporator of an automobile air conditioning system to be cooled, water vapor contained in the air condenses on the surfaces of the evaporator and on surrounding surfaces. During normal operation of the vehicle, the water that condenses on the evaporator simply runs to the bottom of the evaporator and is drained from the air conditioning system onto the roadway. However, when the vehicle's engine is shut off and the air conditioning is no longer in operation, the condensed water on the evaporator begins to evaporate slowly within the ductwork of the air conditioning system and, as a result, a damp dank atmosphere is created. Such an atmosphere is ideal for the growth of mold, mildew, fungus, and bacteria within the ductwork of the system and particularly on the moist and wet surfaces of the evaporator. The growth of such organisms, in turn, results in a stale and unpleasant odor within the passenger compartment itself and can lead to air-borne spores and other organisms that are unhealthy for the occupants of the vehicle.
In the past, there have been attempts to address the problems of microorganism build-up within automotive air conditioning systems. For example, disinfectants and/or deodorizers may be sprayed into the air conditioning system to coat the surfaces thereof to prevent the growth of mold, mildew, and other fungus and bacteria within the ductwork. While this approach can prevent the build-up of odor causing organisms or mask their odors, at least in the short term, it still does not address the fundamental cause of such build-up, i.e., the moist, damp atmosphere within the air conditioning system.
The invention disclosed and claimed in the incorporated reference approaches the problem by preventing the establishment of a moist atmosphere within the air conditioning system that is conducive to the growth of unwanted microorganisms. In general, this invention comprises a method of drying the interior and evaporator of a vehicle's air conditioning system to thwart the propagation of fungus and bacteria and its attendant odor. The method comprises the steps of determining that the engine of the vehicle has been switched off, determining that the air conditioning system was in operation prior to the engine being switched off, and, upon determining that both of these conditions exist, operating the blower of the vehicle's air conditioning system on a predetermined time schedule to draw air through the system for drying condensate from interior surfaces thereof. To carry out this methodology, the incorporated reference discloses an electronic control circuit coupled to the blower motor of the vehicle air conditioning system. When the circuit senses that the engine has been shut off after air conditioning operation, it activates a relay on a predetermined time schedule, such as once every ten minutes, for a predetermined period of time. The intermittent scheduled operation of the blower draws out and removes evaporated condensate from within the air conditioning system and, at the end of several cycles, all of the condensate has been dried and removed. Thus, the fundamental cause of the growth of undesirable microorganisms, i.e., the moist, damp atmosphere within the air conditioning system, is eliminated and such organisms do not tend to grow in the resulting dry atmosphere.
Operation of a vehicle's air conditioning blower motor on a predetermined time schedule after operation of the air conditioning system as disclosed in the incorporated reference has proven to be a successful solution to the problems of micro-organism growth and its attendant odor in vehicles. However, the Electronic Evaporator Dryer (EED) circuitry taught in the incorporated reference for carrying out the methodology, while very successful for use within some automotive blower wiring schemes, nevertheless is not useable with certain other wiring schemes found in the automotive industry. More particularly, the relay of the EED circuitry in the incorporated reference is spliced into the blower motor circuit downstream of positively switched blower control circuits of the system. The other terminal of the blower motor is connected directly to ground in these “positively switched” systems. During the drying operation, the relay of the EED circuit is activated to disconnect the positive terminal of the blower motor from the blower control circuitry and to connect it to directly to the positive terminal of the vehicle's battery. Thus, when the relay is activated, the blower motor is operated at maximum speed to dry interior surfaces of the air conditioning system. Operation of the blower at its maximum speed is highly desirable to achieve the best and quickest drying.
While the foregoing EED circuitry works well for systems wherein the blower motor is positively switched, i.e. switched and controlled on the positive side of the motor, it does not operate well in systems where the blower control circuitry of the air conditioning system is “negatively switched” or, in other words, switched to ground. In such a negatively switched system, the positive terminal of the blower motor normally is connected directly to the accessory switch of the vehicle and the negative terminal of the blower motor is connected to ground through the blower control circuit. The blower control circuit includes a blower switch for turning the blower on and off and an array of resistors for controlling the speed of the blower motor as it runs during normal operation of the vehicle.
Thus, during the drying operation, if the positive terminal of the blower only is connected through the EED relay to the positive terminal of the battery, the blower motor in most cases will not operate at maximum speed because the negative terminal of the blower is connected to ground through the speed control resistor network of the blower control. In some cases where a driver has turned the blower to the “off” position in a negatively switched scheme, the blower, using the EED circuit of the incorporated reference, will not operate at all during the evaporator drying cycle. Thus, there is a need for an improved EED control circuit for carrying out the methodology that is applicable to and works with blower motor wiring and control schemes wherein the blower motor is positively switched and controlled and also works with wiring schemes wherein the blower motor is negatively switched and controlled. It is to the provision of such a circuit and the methodology carried out by the circuit that the present invention is primarily directed.